Problem: Determine how many solutions exist for the system of equations. ${-3x-y = -9}$ ${y = -10+x}$
Solution: Convert both equations to slope-intercept form: ${-3x-y = -9}$ $-3x{+3x} - y = -9{+3x}$ $-y = -9+3x$ $y = 9-3x$ ${y = -3x+9}$ ${y = -10+x}$ ${y = x-10}$ Just by looking at both equations in slope-intercept form, what can you determine? ${y = -3x+9}$ ${y = x-10}$ The linear equations have different slopes. ${1}$ ${2}$ ${3}$ ${4}$ ${5}$ ${6}$ ${7}$ ${8}$ ${9}$ ${\llap{-}2}$ ${\llap{-}3}$ ${\llap{-}4}$ ${\llap{-}5}$ ${\llap{-}6}$ ${\llap{-}7}$ ${\llap{-}8}$ ${\llap{-}9}$ ${1}$ ${2}$ ${3}$ ${4}$ ${5}$ ${6}$ ${7}$ ${8}$ ${9}$ ${\llap{-}2}$ ${\llap{-}3}$ ${\llap{-}4}$ ${\llap{-}5}$ ${\llap{-}6}$ ${\llap{-}7}$ ${\llap{-}8}$ ${\llap{-}9}$ When two equations have different slopes, the lines will intersect once with one solution.